Our current understanding of the pathogenesis of HIV-induced neurocognitive impairment (NCI) centers on the migration of activated inflammatory monocytes (MO) through the blood brain barrier (BBB) into the brain. We recently conducted a small, 24 week, single-arm, pilot study of subjects on stable antiretroviral therapy (ART) with Maraviroc (MVC, Selzentry(r)), a negative allosteric inhibitor of the CCR5 receptor. We found in a preliminary study that MVC intensification led to a reduction in HIV-infected MO (decrease in intracellular HIV DNA in CD14+ cells); a decrease in MO activation (lower frequency of CD16-expressing MO subsets); decrease in CD8+ T cell activation (lower % of CD38+HLA-DR+ CD8+ T-cells); and crucially an improvement in neuropsychological (NP) performance among subjects who had mild/moderate NCI. We now propose a randomized, placebo-controlled, 48 week study of MVC intensification in 42 HIV infected subjects on ART with mild to moderate NCI and include neuroimaging and immunology assays. We will assess 48 week change in NP performance as the primary endpoint and will examine the cascade of events important to the pathogenesis of HIV NCI. We will assess change in MO phenotype, HIV DNA burden and function; and changes in neuronal and inflammatory brain metabolites by multi-voxel Magnetic Resonance Spectroscopic Imaging (MRSI). We focus this proposal on the role of MO based on published literature hypothesizing a key role for these cells in HIV NCI and on the results of our preliminary data that MVC appears to induce a decrease in MO immune activation and in the number of HIV infected MO (HIV DNA within CD14+ cells) within the bloodstream. We hypothesize that a decrease in activated MO subsets will be observed following MVC use. We will extend our data by assessing HIV DNA levels not only in MO (CD14+ cells) as a whole, as was done in our preliminary data, but within each subset. Finally, in an exploratory aim, we propose to non- invasively assess whether MVC impacts brain markers of inflammation and neuronal health using MRSI, a MRS neuro-imaging technology capable of assessing metabolites across an entire 2-dimensional image of the brain.